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 That means methane may be a bigger global warming issue than
thought, scientists say. Methane is 21 times more potent at trapping
heat than carbon dioxide, the most abundant global warming gas,
although it doesn't stay in the air as long.
Much of that extra methane, also called natural gas, seems to be
coming from livestock, including manure, belches, and flatulence, as
well as leaks from refining and drilling for oil and gas, the study
says. It was published Monday in the Proceedings of the National
Academy of Science.
The study estimates that in 2008, the U.S. poured 49 million tons of
methane into the air. That means U.S. methane emissions trapped
about as much heat as all the carbon dioxide pollution coming from
cars, trucks, and planes in the country in six months.
That's more than the 32 million tons estimated by the U.S.
Environmental Protection Administration or the nearly 29 million
tons reckoned by the European Commission.
"Something is very much off in the inventories," said study
co-author Anna Michalak, an Earth scientist at the Carnegie
Institution for Science in Stanford, Calif. "The total U.S. impact
on the world's energy budget is different than we thought, and it's
worse."
EPA spokeswoman Alisha Johnson said her agency hasn't had time to go
through the study yet, but hopes it will help "refine our estimates
going forward."
While the world has a good handle on how much carbon dioxide is
pumped into the air, scientists have been more baffled by methane
emissions. They have had to use computer models to estimate how much
methane is going into that air.
This study, however, was based on nearly 13,000 measurements from
airplane flights and tall towers, the most used in any such
research.
The information was collected in 2008. Scientists have yet to
analyze their data from 2012, and that will capture more of any
impact of the natural gas boom from hydraulic fracturing, Michalik
said. Studies recently have shown conflicting results about how much
methane escapes during fracking and other forms of fossil fuel
drilling.
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Outside experts praised the study. Robert Howarth at Cornell
University called "it very compelling and quite important. This is
the most comprehensive study yet."
Michalak said because of the way they measured methane — just
looking for it in the air as opposed to tracking it from a source —
it is hard to say what is putting more methane into the air. But she
said by looking at concentrations — especially within Texas,
Oklahoma and Kansas — the scientists have a good idea: cows, oil and
gas.
Nearly one-quarter of the U.S. methane emissions came from those
three states. Texas is by far and away the No. 1 state for
refineries that turn oil into gasoline. Texas and Oklahoma have been
big oil and gas drilling states and Kansas is a big cow state.
Cows seem to be spewing twice the methane than scientists previously
thought, Michalak said.
While burps and flatulence are part of the methane emission from
cattle, University of California Santa Barbara professor Ira Leifer
said a bigger factor is manure.
"If you shovel it into an artificial lagoon, you are creating the
perfect production for methane, but it cuts down on the smell and
your neighbors complain less," he said.
___
Online:
Journal: http://www.pnas.org/
[Associated
Press; SETH BORENSTEIN, AP Science Writer]
Seth Borenstein can be followed at
http://twitter.com/borenbears.
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